Robin: Wow. When did you guys start to notice that he was kind of dumb?
Barney: Well, there was the time Nick was doing the crossword.
[flashback to Robin and Nick with Barney at MacLaren's:]
Nick: Hey, what's a four-letter word for "cut"?
Barney: Nick.
Nick: Yeah?
Lily: Is a four-letter word for "cut."
Nick: What is?
Marshall: Nick.
Nick: What? Oh. I got it. Shave.